In the early personal computers, users could only open, see and edit one file at a time. With the invention of graphic user interfaces in advanced operating systems, users were able to see and edit side-by-side two or more different open files. As graphical user interfaces became more sophisticated and different types of files became popular such as Microsoft Word and Excel, Adobe's PDF, etc. the technology evolved to allow replacing by default the icon that graphically represented the file by the file contents themselves. For example, some personal computers today display the first page of the PDF document as the icon that represents the small thumbnail of the PDF document. In addition, if the user hovers on top of a particular thumbnail of a multipage PDF file, a pair of arrows going back and forward appears, and the user may navigate inside that thumbnail and see a miniature version of all the pages in the PDF file, one file at a time.
If a user wants to edit or make a marking annotation on the PDF thumbnail, the user must first open the PDF file itself and then proceed to edit or mark the file. If the user wants to compare two or more files, he/she needs to also open the next file to edit and position them side by side to either compare or work on them simultaneously. Once the user has finished the editing, he/she may need to save the files. The saved files continue to be displayed on the graphic interface as only a thumbnail representation.